In Ancestry sometimes you have to separate the Mc. Ths Mc Lachlan works - don't ask me why.
In 1871 she is Ellenor J Mclachlan married 24 in Kirkdale, Liverpool, with a son, William. 9 months b Liverpool, but no husband present.
However in the June quarter of 1868 in West Derby there is a William McDonald and an Ellen McDonald on the same page in the marriage index Vol 8b page 591.
THE IGI has a Castletown christening on August 21 1845, daughter of William McDonald and Anne.
William McDonald married Anne Corrin in Malew on February 22 1846.
I did not have time to track this family in 1851 and 1861.